The present invention relates generally to robotic gripping devices. More particularly, the invention concerns a method and apparatus to grasp containers of varied sizes using a plurality of movable fingers
Many industries rely upon automated handling of bottles, vials and tubes of different sizes. In many applications, the ability to handle different size containers is provided by a rotating turret assembly with a number of different size openings arranged on a circular assembly. The turret is rotated to select the opening with a size that matches a selected container size. In other applications, rather than requiring the selection from multiple handlers to accommodate each different size container, attempts have been made to provide adjustable grippers which operate by moving two to more fingers inward and outward relative to a center point at which the container is located. Typically, the fingers are pneumatically actuated. The fingers may either move on fulcrums, like “pincers”, so that the angles of the gripping surfaces change, or they can slide along a single plane so that the fingers remain parallel with the distance between the fingers being adjusted to fit the container diameter. In one example, the gripper mechanism described in U.S. Pat. No. 6,592,324 of Downs et al uses a combination of sliding and rotation of two arms to pin microplates. While such systems may work well with containers of a consistent size, the force applied to the container can vary depending on the size of the container. These failings are particularly pronounced in applications involving the storage of compounds, biological specimens or other samples. Such storage systems hold many thousands of samples which may be in different size glass or plastic vials or tubes and may have different closure means, such as stoppers inserted into the opening and caps or adhesive films covering the edges of the openings. The gripper robotics are often contained within an environmentally-controlled enclosure, making frequent changing of the gripping mechanism to fit a particular container impractical. Since the containers usually hold very small volume samples, these vials and tubes can be small and relatively fragile. One of the problems that can occur with variable force control on current the commercially-available grippers is that sometimes the caps or tubes are broken or are not gripped sufficiently well. These grippers are also incapable of self-adjusting for different cap sizes. Another problem is that pneumatic grippers do not produce sufficient feedback to let the system know if a tube of the expected dimensions was, in fact, picked up.
In view of the shortcomings of existing grippers, the need remains for a container gripper that has the ability to adjust to a range of container sizes and surfaces, and which provides feedback to allow control of the force applied to the container. The present invention is directed to such an invention.